Original Xbox. It was in a generation where it never stood a real chance to compete with the behemoth PS2, but they still come out offering a good amount of great games not available on other platforms. Along with a great online infustructure compared to the far less streamlined DC and PS2 methods.
360 had a great few years at the start, but that's mostly down to PS3 being a bit of a damp squid for a while. As soon as 2008-9 hit, Sony woke up and started to better the 360 for the remainder of that gen with far better first party offerings. Instead of Xbox sticking with a good thing, they decided to shit the bed with Kinnect bollocks, which then lead into the worst console unveiling of all time with the Xbone.